Insertion of unsaturations into the 1,4,7-triazacyclononane skeleton. Photochemical reaction between benzil and diethylenetriamine: synthesis and properties of 2,3-diphenyl-1,4,7-triazacyclonona-1,3-diene

Photochemical reaction between benzil and diethylenetriamine (dien) in anhy drous methanol in the presence of oxygen yields a novel triaza macrocycle 2 ,3-diphenyl-1,4,7-triazacyclonona-1,3-diene (L). It was characterised by FT IR, EI mass and NMR (H-1 and C-13) spectra. A comparative study between the various physicochemical properties of L and the product (L-1; reported ear lier by others) of the thermal reaction between benzil and dien is made in detail. L and L-1 can be regarded as isomers. While L-1 cannot be converted to L by UV radiation, L is transformed into L-1 upon refluxing in anhydrou s methanol. The macrocycle L affords cationic copper(i) complexes of the ty pe [CuL]X (X=ClO4- and PF6-). Cyclic voltammetry and coulometry at platinum electrodes in dimethylformamide under an N-2 atmosphere show that the Cu-I I/I potential in [CuL]X is 0.25 V vs. SCE. This indicates that L is a weak pi-acid. L is photoluminescent in methanol at room temperature (emission ma xima lambda(em)=380 nm; quantum yield phi=1.96x10(-2)). Its emission when i n the form of [CuL]X in methanol is quenched considerably (lambda(em)=370 n m; phi=6.2-6.7x10(-3)).